Electrical variable capacitance device with auxiliary



Aug. 2, 1949. v s R N- M 2,478,120

ELECTRI MOV R OUT INVENTOR i FIG.2

Patented Aug. 2, 1949 ELECTRICAL VARIABLE CAPACITANCE' DEVICE WITHAUXILIARY Surrius Rector: Montcalm Signor to Ferris ,tzBoonton, N. J.,as-

Instrument Laboratories,

Boonton, N. J., a corporation of- New Jersey ApplicationFebruary '7,1945, Serial No; 576,617

3 Claims. 1

My present invention broadly relates to an electrical capacitance-deviceand more particularly to such a device designed particularly tofunctionias an auxiliary'to a primary electrical capacitance devicawithboth of the devices being capablecfwidely-varying their respectivecapacitance values."

An object or my-presentinvention is to have the stators' of a' primarycapacitance device also serve asthe-stators'of my herein described andclaimed auxiliary electrical capacitance device.

In 'the art of dealingwith electrical alternating currents in mannerscalling for using tunable electrical circuits-over wide and quite oftenvery wide ranges of irequencies, the resonant frequencies of whichcircuits are m'ore often than not controlled by variable electricalcapacitance devices commonly" termed variable condensers, itoften'becomesdesirable and/ or necessary to make small'changes intheresonating status of one'or more-circuits, and particularly sowherea-plurality of'suoh circuits are -'so connected in cascade as to operatein. response to the same electrical alternating currents with alldependin upon the same single adjustment in an 'eifort tomake all of'the circuits involvedequally resonant at each of the samefrequenciesover the wide or very wide range. of frequencies involved,commonly termed resonant tracking. For example, I havebeencalle'd-"upon'to'make three cascade variable electrica-l:circuitsresonantlytrack over the exceptionally'very'wide range' of frequenciesof 'from 20 -t0 250 megacycle's' in orderthatthe special signalgenerator "requiring I this performance can be'relia'bly dependedupon'fo'rchecking the respective over-all performances" of radioreceivers and the like using' these frequencies for the first time i11the-present war":- In 'unde'rtaking to find a suitableanswer to thisunsolved Wartime emergency problem, I'ffoundit to beabsolutelyimperative that the last 'or finalfstage had to be subject to auxiliaryadjustment of its resonant status independent cf-the other stages forthe following wtechnological reasons:

That otherwise there would be an inherent grave diffi'c ulty inmaintainin'g substantially perfoot tracking of the-three circuitsthroughout the extraordinary wide'v range even though the final stage 1worke'd into substantially no load or a substantially constant-load;that, therefore, it

would: be foolish to hope tomaintain substantiallyperfecttrackin'g inthepresence of the variable output loading that could becounted upon in thecase of 'the' operations involved; that the same -=wou-ld be trueinthepresence of the modulation of'the'carrier' currents normal tosignal generator operations; that the adjusting from substantiallya-negli'gible capacitance to the maximum're'quiredwould have to besmooth andsubstant-ia'll'y devoid of-irregularities; that it must notcouple into the circuit any appreciably greater losses in being operatedto increase the capacitanc'e involved than would a correspondingincrease of the primary capacitance; that'it must notcouple intothecircuit any extraneous electrical conductance that would thereby becapable of resonating at any frequencyat which the instrumentalityinvolved is capable of operating; that it should ofitself be fitted forsuch physical adjusting that its maximum capacitancecan be increasedor-decreased to some effective extent; and that it should be simple toadjust and-not likely to get out of order.

With these and other objects that may be readily-apparent in view, andwith the aid of the figures of 'theaccompanyin drawing in which likesymbols refer to parts like in kind or function sofar as practical, thefollowing is a description of-my present invention and how I practicethe same:

Fig," l'illustratesin perspective a majority of the-elements. necessaryto practicing my present invention, and Fig. 2 illustrates across-sectional view'of Fig; 1 on line XX viewed'from its far end 'plusthe necessary elements missing from Fig.- 1.

Referring'to Fig. 1, the elements referable to by the symbols SI, S2,II, I2 and R in the relations-'thereinshown illustrate an electricalvariabl'e'capacitance device illustrated and described in'an-application of Harold E. Barnes, Serial No. 542,192, filed June 26,1944, and referred to by me inan application of mine Serial No. 574,533,filed January 25, 1945, now Patent No. 2,458,187, issued J anuary' l,1949. As clearly displayed, the illustrated elements Si and S2 indicateunusually massive stators of sloping insides havinginterposed-*therebetween an unusually massive rotor of sloping sidesforming an electrical variable capacitance device, the technologicalreasons for which massivenesses in connection with dealing withelectrical alternating currents of the high, very high and ultra highfrequencies within the range of from 20 to 250 megacycles are most fullypropounded in the specification of the said Barnes application, with allof which, from the actual experience therewith I have had, I fullyagree.- However, Fig. 1 further illustrates as an addition to theprimary variable capacitance de- "viceof the'saidBarnes auxiliaryvariable capacitance means comprising a cross-wisely disposed plate CPhaving right-angularly affixed thereto at its respective ends theextending downwardly shaped blades T! and T2 in planes more or lessparalleling the respective outsides of the stators SI and S2. Thevisible hole MI-I in element T2 indicates that the auxiliary variablecapacitance means are subject to being rotatably mounted in the relationshown with respect to the primary variable capacitance device.

Referring to Fig. 2, the element IS illustrates a mounting shaft for theauxiliary variable capacitance means which closely fits in mountingholes MP1 of elements T! and T2, the said means being held in the properposition on the said shaft by the indicated set screw bands MI and M2,and the said shaft being indicated as terminating in an operable knob Kafter passing through an indicated panel W. Fig. 2 further indicatesthat there are air spacings between the element or trimmer Ti and theouter fiat side of the stator SI and the element or trimmer T2 and theouter flat side of the stator S2, and by the oppositely pointing arrowslabeled Moveable In or On that the rotor R is by some suitablemechanism, not shown because of not being a part of my presentinvention, moveable in or out. In other words, because the rotor R isintended to be equipped with means for moving it in or out it forms withstators SI and S2 a primary variable capacitancedevice with thedielectric being the air spaces therebetween.

As to operations, referring again to Fig. 1, the usual electricalcircuit would comprise an electrical inductance element connected acrossthe terminals 1! and 12 which would bring the air spaces between SI andR, and between R and S2, and vice versa, in series to, as is well known,substantially cut in half the amount of capacitance that would otherwiseexist between the elements separated by a single air space assuming thatthe air spaces are substantially equal in all respects; and the samenecessarily holds true irrespective of" the in or out position of therotor R. Certainly, it is easy to understand that to build for and setup two or more such electrical circuits including inductance andcapacitance so perfectly that they would perfectly track at allfrequencies from 20 to 250 megacycles would be utterly impossible, sothat the question naturally arises as to whether or not reaching such agoal should be earmarked as totally outside the realm of humanattainment.

In my heretofore identified patent application it is brought out thatalthough I obtained all of the success required in lining up or trackingtwo 20 to 250 megacycle circuits operating in cascade with another typeof trimming device, I had used a special controllable from the paneltrimmer for the capacitance device in the third circuit. It so happensthat the special trimmer there casually mentioned is the subject of mypresent invention which I found to have been necessary to satisfactorilyreaching the such a goal.

Assuming that as is usual material highly conductive of electricity ispreferably used in the case of all of the parts in which there is activeelectrical current movement or flow without further reference thereto,it is readily apparent from the illustrated dimensions thereof that theelectrical current movements in the elements CP, Tl and T2 meet withvery low resistances so that the main reaction to the electricalalternating current effects reaching them through terminals II and I2and the respective massive stator i capacitive, the inherent distributedinductances therein being so low due to the massive construction used asto be almost negligible in the matter of ei'lectively reacting until thefrequencies become of the very high kind; and it is also readily con entthat this capacitive reaction is in the Cir .nt involved, in parallel toand adds to any temporary capacitive reaction of the primary variablecapacitance device in said circuit. However, it is clearly apparent thatdue to the low resistances met with in said auxiliary elements thiscoupling in of them does not add any losses greater than would be addedif the primary capacitance alone was responsible for the particularcapacitance increase, and that due to the paralleling of the respectiveelements involved it is doubtful that any increase in loss of energytakes place in the circuit involved.

Referring again to Fig. 2, the shaft IS is preferably made of someexcellent electrically insulating material, and it is evident that plateCP, overlapping substantially to the same extent as it does both statorsin addition to being substantially removed therefrom from a capacitancecreating point of view, contributes little or nothing towards the totalamount of any of the auxiliary capacitance herein contemplated; fromwhich it is further evident that if trimmers TI and T2 are rotated so asto be well clear of their respective stators the resulting auxiliarycapacitance will be at a minimum of almost zero, which, of course, canbe done from the knob K. From there on the auxiliary capacitance canreadily be increased to its maximum possible the more the trimmers Tland T2 are made to overlap their respective stators simply by turningthe knob K in'the right direction, and if the maximum turns out to beinsunicient with the planes of the trimmers paralleling their respectivestator sides, an increase in maximum can readily be had by bending thetrimmers towards their respective stators. Furthermore, the rate ofchange of capacitance versus change of angle of knob K can be almostinfinitely controlled by proper shaping of the said trimmers.

Summarizing the advantages of such'an auxiliary capacitance device theyare: easy to produce, install and adjust and not likely to get out oforder; minimum capacitance of almost zero; very low resistances; verylow dielectric losses since the insulating shaft IS of higher dielectricconstant than air is located outside of any strong field; maximumcapacitance obtainable increasable by easy bending of trimmers; rate ofchange of capacitance with angle of rotation easily controllable byproper shaping of trimmers; does not couple to the electrical tunablecircuit any conductor capable of resonating at any frequency at whichthe instrumentality involved is capable of operating; and permits ofproviding for varying its capacitance from a minimum of substantiallyzero to an effective maximum with smoothness devoid of irregularities.

Although I have described the auxiliary capacitance device of my presentinvention particularly with respect to its application to an ultramodern type of primary electrical variable capacitance device, it isclearly also applicable to any type of such device in which suitablesurfaces are available if the amount of variation desired is not outsideof the amount that can be obtained without introducing the danger ofencountering a tendency to flash over.

Normally, the cascaded circuits with which I have dealt would each be ina separate compartment highly-shielded=fr0m--everything else and allin a:totally enclosing-housingaalsolcapable of effectively shielding thewhole, from=the-outr side, so that the lining up of the first twocircuits would *have'tobe'undertakenbefore the housing is finally fullyclose'dnwith it also'being madeecertain that the third=and.final:circuit is lined up clio'se enough to makefinal commercially acceptablelining up from-the panel knob possible.

While I have described my present invention in certain confinedrespects', it is apparent: that modifications maybe made. and -.:that no:limitations are intended other than those imposed by the scope of theappended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. In association with a primary variable electrical capacitance devicesuitably constructed for providing the major ccrnponents of capacitivereactions in an electrical circuit that with suitably selectedinductances is called upon to resonate at frequencies ranging from theorder of 20 megacycles to the order of 250 megacycles in which theconstruction includes two stators and an interposed therebetweenvariable rotor all of such low resistance material in such massivequantities of it that the consequential inherent distributed inductancesset up thereby are so low that even at frequencies of the order of 250megacycles some small but tangible amount of external inductance can beused in the circuit involved without the essential amount of circuitinductance for maintaining operations at such frequencies beingexceeded, said stators each preferably having one of its major surfacesflat in a plane paralleling the plane of the other: the combination ofmeans constructed and operable for acting with said primary device as anauxiliary variable capacitance device to change the tuning of saidcircuit to thereby bring about resonance of it when further movement ofsaid rotor of said primary device is desirable, comprising a platepreferably made of a very low electrical resistance material long enoughto span with margin to spare the distance between said flat statorsurfaces having preferably integral therewith at each of its endssubstantially duplieating, specially shaped blades extending in the samedirection in planes substantially paralleling said stator surfaces, saidplate and blades having adequate cross-sectional dimensions for makingthe reactions of the same to the electrical alternating effects shuntedtherethrough mainly capacitive and thereby free enough of resistances toassure effective operation throughout said range of frequencies; andmeans for supporting said plate at a material distance from said statorsand rotor and rotating it and its afiiXed blades in substantiallyduplicating relations to said stator surfaces comprising a supportedshaft of preferably excellent insulating material extending throughclosely fitting holes in corresponding places in respective parts ofsaid blades near their respective junctions with said plate, said shaftbein preferably terminated at one of its ends with enlarged means forfacilitating its being rotated.

2. In an electrical variable capacitance device for creating withsubstantial precision the necessary variable capacitive reactions in anyelectrical circuit designed to resonate with substantial precision athigh, very high and ultra high frequencies which has provisions formajorly and minorly varying said reactions independently ofhighfrequency current flows therein that some low but tangible amount-ofcircuit inductance for maintaining operations at said frequencies may beused-without exceeding the necessary amount of circuit inductancerequired for resonating at the highest of the ultra high frequenciesbeing used, which said capacitance elements provide for majorly varyingthe capacitance reactions involved; and a plate preferably made of avery low electrical resistance material long enough to span with marginto spare the distance between the sides of said stators facing away fromsaid sloping sides of the same having preferably integral therewith ateach of its ends substantially duplicating, specially shaped bladesextending in the direction in planes substantially paralleling said lastnamed stator surfaces, said plate and blades having adequatecross-sectional dimensions for making the reactions of the same to theelectrical alternatin effects shunted therethrough mainly capacitive andthereby free enough of resistances to assure effective operationthroughout said range of frequencies; and means for supporting saidplate at a material distance from said stators and rotor and rotating itand its affixed blades in substantially duplicating relations to saidstator surfaces comprising a supported shaft of preferably excellent insulating material extending through closely fitting holes incorresponding places in respective parts of said blades near theirrespective junctions with said plate, said shaft being preferablyterminated at one of its ends with enlarged means for facilitating itsbeing rotated; which said last named capacitance elements together withsaid stators provide for independently and minorly varying thecapacitance reactions in the circuit involved.

3. A variable capacitance cal circuit adapted for very precisely tuningthe same in co-operation with interchangeable different valueinductances over a frequency range of the order of 200 megacyclescomprising: the combination of two unusually massive statorssufiiciently spaced to accommodate a correspondingly unusually massive,movable with respect thereto rotor to thereby make the capacitancerelations between said rotor and stators adaptable for acting in an inseries relation; an elongated, highly conductive of electricity plate ofsuflicient length to at least span the distance between the respectiveoutsides of said stators; specially shaped for the purpose, highlyconductive of electricity blades right angularly terminating therespective ends of said plate in planes adjacent to and substantiallyparalleling said outsides of said respective stators to thereby make thecapacitance relations between said stators and blades adaptable foracting in an in series relation in parallel to said capacitancerelations between said rotor and stators, said device for anelectriplate and blades having adequate cross-sectional dimensions formakin the total reactions of the same to the electrical'alternatingefiects shunted therethrough mainly capacitive and thereby free enoughof resistances to assure effective operations of the same inco-operation with said. rotor and stators throughout said range offrequencies; and'means for supporting and rotating said plate and bladescombination to thereby make said. capacitance relations with saidstators adequately variable for the purpose intended comprising asupported shaft of electrical insulating material extending throughclosely fitting holes in corresponding places in respective parts ofsaid blades near their respective junctions with said plate,

saidshaft being terminated at one of its ends by means facilitating itsbeing rotated.

SURRIUS HECTOR MONTCALM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,872,299 Kerrigan Aug. 16, 19321,983,379 Leach Dec. 4, 1934 2,041,186 Jacobson May 19, 1936 FOREIGNPATENTS Number Country Date 258,323 Great Britain Sept. 13, 1926

